A proton exchange membrane (PEM) fuel cell, also known as a polymer electrolyte membrane (PEM) fuel cell, uses fuel, e.g., hydrogen, and oxidant, e.g., oxygen from the air, to produce electricity, by transforming the chemical energy liberated during the electrochemical reaction of the fuel and oxygen to electrical energy. A PEM fuel cell generally employs a membrane electrode assembly (MEA). The membrane electrode assembly (MEA) includes a PEM disposed between two electrically conductive electrode plates, an anode plate and a cathode plate. The anode plate may include an anode gas diffusion layer and an anode catalyst layer. The cathode plate may include a cathode catalyst layer and a cathode gas diffusion layer. The electro-catalyst is typically disposed at each membrane/electrode plate interface to induce the desired electrochemical reaction. Each electrode plate includes a fluid flow field for directing the fuel and the oxidant to the respective electro-catalyst layers, specifically, at an anode on the fuel side and at a cathode on the oxidant side.
The fuel flow field directs a fuel stream to the anode. The fuel stream migrates through the porous anode gas-diffusion layer, and is oxidized at the anode electro-catalyst layer. The oxidant flow field directs an oxidant stream to the cathode. The oxidant stream migrates through the porous cathode gas-diffusion layer and is reduced at the cathode electro-catalyst layer. In a PEM fuel cell that uses hydrogen as fuel, the hydrogen is oxidized at the anode to produce protons. The protons migrate through the MEA and react at the cathode with an oxidant such as oxygen to produce water as the reaction products.
The water produced by the reaction may accumulate at the cathode, due to the electro-osmotic drag of water molecules by the protons passing from the anode through the MEA to the cathode. This water is commonly referred to as “proton drag water.” The proton drag of water from the anode to the cathode results in a lower water concentration on the anode side of the PEM compared to the cathode side. If the PEM does not remain highly saturated with water, the PEM resistance increases, and the power obtained from the fuel cell decreases. At the cathode, the accumulated water may impede and could prevent oxygen from reacting with the protons ions and electrons. Accumulation of water in the cathode thus also reduces the electric potential created across the fuel cell, thereby limiting the fuel cell's performance. Therefore, it is desirable to promptly move the water from the cathode side to the anode side.
The disclosed system is directed to overcoming one or more of the problems set forth above.